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  <meta charset="UTF-8">
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  <title>Document</title>
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<body>
  <script>
    let arr = [5, 8, 9, 2, 1, 5]
    let sum = 0
    for (let i = 0; i < arr.length; i++) {
      // arr[i]是arr数组中的每一个数据
      sum += arr[i]
    }
    console.log(sum);
  </script>
</body>

</html>